The present invention relates to an implant for permanent or temporary incorporation into the human or animal body and a placeholder for vertebrae, an intervertebral disc replacement or a connecting rod for pedicle screw arrangements as well as a stabilization system made from these components.
In modern medicine, use of implants to replace parts of the human skeleton following illness, injury or age-related wear-phenomena is widespread. Thus, it is known, for example, in the case of spinal injury such as breaks or when parts of the spinal column are attacked by a tumour, corresponding vertebrae are replaced by placeholders. Such placeholders are described, for example, in European patent EP 0 268 115 B 1.
In a similar manner, intervertebral discs may be replaced by corresponding placeholders, such as described in DE 43 23 034 C1. These placeholders, which generally have a cylindrical tubular base structure, must essentially accommodate axial compressive forces in order to dissipate the forces that are borne by the spinal column. To this end, such placeholders must have adequate strength.
Additionally, a certain amount of flexibility in placeholders may be needed in order to provide movements of the spinal column, especially bending or twisting. For this purpose, prior art placeholders for vertebrae or intervertebral discs provide a combination of the two functionalities, namely strength on the one hand, especially in the axial compressive direction and mobility, and on the other hand, bendability about a rotary axis at right angles to the direction of axial load. Examples of this are DE 103 37 088 A1 and WO 2005/039454 A2. In the case of these placeholders, the central region between the ends, which serve the purpose of arrangement or attachment in adjacent tissue or adjacent vertebrae, has a flexible region, which is achieved either by corresponding elastic materials or by a corresponding structure of the placeholders. WO 2005/039454, for example, discloses a spiral-shaped circumferential slit, which imparts spring-like properties to the base body in the elastic central region.
WO 2005/039454 A2 further discloses that other implants, such as connecting rods for pedicle screw arrangements or similar stabilization systems, may have a certain flexibility derived from corresponding helical shapes, in addition to an ability to transmit forces.
Although these solutions yield very good results with regards the attainable flexibility, deficits concerning the strength and the extent of the axial compressive load that can be accommodated still exist.
Therefore a need for a placeholder that provides opposite functionalities is given. The functionalities comprise primarily flexibility and mobility. In addition, there must be a strength or load bearing capacity. Further, the implant, e.g. the placeholder should be simple to manufacture and should allow easy handling during surgery.